1. Field of the Invention
This invention relates, broadly speaking, to injection molding of thermosetting polymers.
More particularly, this invention relates to gas assisted injection molding of thermosetting polymers.
Even more specifically, this invention relates to gas assisted injection molding of polyester thermosetting polymers.
2. Description of the Prior Art
Gas assisted injection molding (commonly referred to as xe2x80x9cGAIMxe2x80x9d) has been labelled one of the most significant manufacturing advancements of the past forty years. Through the manipulation of injected polymer and pressurized gas, innovators have improved plastic part quality while, in many cases, reducing processing and material costs.
GAIM was developed, in part, to reduce the volume of thermoplastic polymers required to manufacture components with thick cross sections. Aside from the economies derived from reduced material requirements, GAIM aids in the elimination of molded in-stress (cracks, warpage), sink marks and unpredictable physical properties (internal stratification). Reduced cycle times are also a benefit, allowing cavity requirements (thus tooling investment) to be reduced by 50% or more.
GAIM has been practiced almost exclusively by the manufacturers of thermoplastic components. The cost advantages associated with GAIM have provided opportunities for more expensive thermoplastic materials to replace low cost thermosetting materials. Even high heat applications, traditionally dominated by thermosetting polymers, are beginning to be penetrated by gas-assisted thermoplastic polymers. The savings realized by reduced tooling, cycle times and material consumption are driving this transition. Molders using thermoplastic polymers several times as expensive as equivalent thermosetting polymers can make parts that cost less using GAIM techniques.
For over a decade, manufacturers of parts made of thermosetting polymers have been faced with the market challenges associated with GAIM. Although there have been some notable gains using phenolic materials, no thermoset technology has shown the quality, repeatability and economies demonstrated by thermoplastics. Up until recently, the thermoset processor""s option was to relinquish margin or lose market share.
The inventors have completed a series of trials that have yielded high quality thermoset parts using gas-assisted injection molding techniques.
One of the objects of this invention is to provide an improved method and apparatus for injection molding of thermosetting polymers.
Another of the objects of this invention is to provide an improved method and apparatus for gas-assisted injection molding of thermosetting material.
A particular object of this invention is to provide an improved method and apparatus for gas-assisted injection molding of polyester thermosetting material.
Still other and further objects of this invention will become apparent by reference to the accompanying specification and drawings, and to the appended claims.
The foregoing objects are attained in part by providing a mold with a gas injection pin at a location remote from that point in the mold where the thermosetting polymer is introduced, i.e., at the end of flow of the thermosetting polymer in the mold.